Apparatus and method for coding/decoding scalable shape binary image, using mode of lower and current layers

ABSTRACT

All macro blocks (MB) decided as an “all_0”, “all_255” or “intra predicted” mode are transmitted as an “intra not coded” mode. A receiving terminal also separates “all_0”, “all_255” and “intra predicted” from the “intra not coded” mode, referring to pixels of a lower layer. “Inter coded &amp;&amp; MVD=0” and “Inter coded &amp;&amp; MVD!=0” modes are represented as “Inter coded”, and “Inter not coded &amp;&amp; MVD=0” and “Inter not coded &amp;&amp; MVD!=0” modes are represented as “Inter not coded”. As its result, coding modes on an I-picture can be reduced to two modes and coding modes on a P-picture, or a B-picture, can be lessened to four modes.

This application is a Divisional of U.S. patent application Ser. No.09/113,008 now U.S. Pat. No. 6,351,563 filed Jul. 9, 1998.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a coding and decoding of binary images,and more particularly, to a method for coding and decoding scalablebinary images by using modes of lower and current layers, which iscapable of reducing coding modes of the binary images by considering acorrelation between the lower and current layers and lessening a codingbit quantity by assigning mode coding bits according to its correlation.

2. Discussion of Related Art

The scalable shape coding has a function capable of transmitting aplurality of layers having different resolution from each other, a baselayer and an enhancement layer, and decoding it. In transmittinginformation having a multiple of different resolutions, more informationshould be transmitted than in a general coding method.

In order to reduce the quantity of transmission information, a methodfor estimating an enhancement layer of the high resolution is appliedthereto by utilizing a base layer of the lower resolution as shown inFIG. 1.

In executing the scalable shape coding for binary image informationthrough a use of plural layers, an effective coding may be also done byemploying the base layer like the aforesaid or using, on the enhancementlayer, the lower layers in case several layers are constructed.

FIG. 1 shows a scalable shape coding method for general imageinformation.

It is herewith represented only one step on an enhancement layer but theenhancement layer of several steps is generally included therein. Thus,a lower layer placed right under a current layer may be a base layer orone layer out of enhancement layers. The scalable shape coding methodfor binary image information has the same structure as a generalscalable shape coding method.

In order to code an enhancement layer for a binary image, in case it isthe enhancement layer for an intra-picture, the enhancement layer iscoded by predicting its just lower layer as shown in FIG. 1. In coding apredicted-picture of the enhancement layer, the coding is performed bypredicting from, both of an image of the just lower layer and a previousimage.

In a coding process of image information, a coding of a block unit,namely a size of 16×16, is done. In coding blocks for the binary imageinformation, namely macro blocks (hereinafter, referred to as ‘MB’), anintra MB on an I-picture or a P-picture on the enhancement layer iscoded by using a scan interleaving method presented on VM(VerificationModel) 7.0 of the ISO/IED WG11, wherein the MB should be coded by usingonly its own lower layer, not using a prediction on a previous image.Its exceptional MBs are coded by using a context-based arithmeticencoding (CAE) method as a coding method of a base layer.

FIG. 2 provides a scan interleaving method.

In order to code an enhancement layer on a base layer, values of twopixels adjacent to each other on the lower and top sides are used. Iftwo adjacent pixel values are same, there is much possibility that apixel at a current position has the same value. Therefore, in case thetwo adjacent pixel values are same and the current pixel has a valuesame as the two adjacent pixel value, a coding is not necessary.

In case two pixel values are different from, the pixel value at thecurrent position should be coded and such a case is said a transitionalsample data (TSD). In case that the two adjacent pixel values are samebut the pixel of current position has not the same value, the codingshould be also done. Such a case is said an exceptional sample data(ESD). Namely, in order to code the enhancement layers by using the scaninterleaving method, two kinds of data, TSD and ESD, should be coded.

To code the TSD and ESD in coding by using the scan interleaving method,information for an existence or non-existence of the ESD is firsttransmitted, and an applicable range of the scan interleaving isdifferent according to an MB having the ESD and an MB not having theESD.

FIGS. 3(a) and 3(b) provide contexts used in the CAE method.

As shown in FIG. 3(a), a context index Context_ID is decided accordingto a position of a context made up of neighboring pixels surrounding acoding pixel X. In order to transmit information for X and Y positions,a coding is performed by employing an arithmetic coding table previouslydecided according to the occurring frequency number of a context indexContext_ID type which is constructed with C0 to C6.

Like this, the MB not used in the scan interleaving method is coded byutilizing a method such as a coding of the base layer, e.g., the CAEmethod. An inter MB on a P-picture of the enhancement, among them iscoded by predicting from a previous image by using a motion vector.

In another case, namely, in case all pixels within an MB have a value of‘0’ or a value of ‘255’, only additional information, mode informationsuch as “all pixels are ‘0’” or “all pixels are ‘255’”, is transmittedwithout coding. Since the coding image herewith is the binary image,each of the pixels may have only two values as ‘0’ or ‘255’. In general,‘0’ indicates a background and ‘255’ represents an object.

That is to say, in order to encode the binary images, a coding method isdifferently decided according to each MB, and the additionalinformation, namely the mode information such as what coding method wasused for a coding of each MB, should be transmitted. At this time, it isneeded a sort for the additional information and a table for codes ofthe additional information, the codes being a first shape code.

The construction of the existing additional information indicating themodes for the enhancement layer of the I-picture, P-picture andB-picture is as follows.

Modes of Enhancement Layer on I-picture

1) all_(—)0: all pixels within MB becomes a background (“0”)

2) all_(—)255: all pixels within MB becomes an object (“255”)

3) intra coded: If ESD (Exceptional sample data) exists, all pixelswithin MB are coded by using the scan interleaving method. If the ESDdoes not exist, only TSD (Transitional sample data) is coded by the scaninterleaving method.

Modes of Enhancement Layer on P-picture or B-picture

1) all_(—)0: the same case as the above-mentioned

2) all_(—)255: the same case as the above-mentioned

3) Intra coded: the same case as the above-mentioned

4) Intra not coded

5) Inter coded && MVD=0

6) Inter not coded && MVD=0

7) Inter coded && MVD!=0

8) Inter not coded && MVD!=0

Data coded as the above is decoded as follows. The additionalinformation indicating the modes is represented at the first position ofa bitstream in each MB of the binary image. The mode information isfirst read on the bitstream in order to decode each of the MBs.

There is constructed a coding table for transmitting the existingadditional information for the enhancement layer of the P-picture andB-picture. In such construction, in order to lessen the number of bits,the coding table is made by predicting from a lower layer or a previousimage. In its construction method, the coding table is constructed by acase that a corresponding MB of just lower layer is “all_(—)0” or“all_(—)255”, and by its exceptional cases.

In case a mode for the corresponding MB of the just lower layer is not“all_(—)0” and “all_(—)255”, the coding table is constructed by a modeof a corresponding MB on the same layer of a just previous image.

Case that the Mode of Corresponding MB for Just Lower Layer is“all_(—)0”

Mode Code (1) 0111 (2) 0110001 (3) 0110000 (4) 010 (5) 00 (6) 01101 (7)011001 (8) 1

Case That the Mode of Corresponding MB for the Just Lower Layer is“all_(—)255”

Mode Code (1)     1′ (2) 0010100 (3)   000 (4) 0010101 (5)   0011 (6) 001011 (7)  00100 (8)    01

In the existing additional information indicating the modes for theenhancement layer per each MB, the I-picture has three sorts asall_(—)0, all_(—)255 and intra coded, and the P-picture has eight sortsas all_(—)0, all_(—)255, intra coded, intra not coded, inter coded &&MVD=0, inter not coded && MVD=0, inter coded && MVD!=0, and inter notcoded && MVD!=0. If the sorts of additional information are many, thenumber of bits representing the respective modes becomes many, thus itmeans that the quantity of transmission bits is many.

FIG. 4 explains a relation between a current layer and a lower layer.Images on the current and lower layers may be same in its size. In casethe size of images are different from each other, all horizontally andvertically may be different from or it may be different in only onedirection. FIG. 4 shows a case different in only horizontal direction.Even though the size of images is different from, the size of each MB onall layers is constant as 16×16. Thus, in case that an image of thecurrent layer is bigger than that of the lower layer, MBs of the currentlayer are included inside an MB of the lower layer, since several MBs ofthe current layer correspond to one MB of the lower layer. That is, animage of the current layer is down sampled and then constitutes an imageof the lower layer.

As shown in FIG. 4, a size of the current layer is twice of the lowerlayer and an MB of the current layer corresponds to a half size of thelower layer MB in this case, the half size being a part of oblique linesin FIG. 4.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method for codingand decoding scalable binary images that substantially obviates one ormore of the limitations and disadvantages of the related art.

An object of the present invention is to provide a method for coding anddecoding scalable binary images, using modes of current and lowerlayers, which is capable of improving a coding efficiency by reducing asort of additional information representing coding methods.

Another object of the present invention is to provide a method forcoding and decoding scalable binary images with modes of current andlower layers, which is capable of lessening coding modes of binaryimages by considering a correlation between the lower layer and thecurrent layer and reducing the quantity of coding bits by assigning modecoding bits according to its correlation.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure as illustrated in the written description andclaims hereof, as well as the appended drawings.

To achieve these and other advantages, and in accordance with thepurpose of the present invention as embodied and broadly described, onlyone mode, an “intra not coded”, instead of three modes as an “all_(—)0”,an “all_(—)255” and an “intra not coded” is used. A transmittingterminal transmits all MBs decided as “all_(—)0”, “all_(—)255” or “intrapredicted” mode, by the “intra not coded” mode. A receiving terminaldiscriminates “all_(—)0”, “all_(—)255” and “intra predicted” from the“intra not coded” mode referring to pixels of the lower layer.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 represents a general scalable shape coding method on imageinformation.

FIG. 2 presents a scan interleaving method.

FIGS. 3(a) and 3(b) set forth contexts used for a context-basedarithmetic encoding method.

FIG. 4 depicts an explanatory diagram showing a relation between acurrent layer and a lower layer in a spatial scalability.

FIG. 5 offers a flow chart providing a method for coding an enhancementlayer of an I-picture in accordance with the present invention.

FIG. 6 illustrates a flow chart showing a method for detecting whetheran image of an enhancement layer is an “Intra not coded” mode in thepresent invention.

FIGS. 7 and 8 are flow charts indicating a method for decoding when modeinformation decoded in a bitstream is an “intra not coded”.

FIG. 9 presents a flow chart for coding a P-image and a B-image of anenhancement layer in the invention.

FIG. 10 provides a method for adjusting a motion vector of a base layeraccording to a ratio of an image size between the base layer and acurrent layer.

FIG. 11 is a flow chart presented in decoding the P-image or B-image ofthe enhancement layer in the present invention.

FIG. 12 shows a block diagram with the construction of an inventivescalable shape coding apparatus.

FIG. 13 gives a block diagram for one preferred embodiment of aninventive scalable shape coding unit.

FIG. 14 furnishes a block diagram showing the construction of aninventive “intra not coded” mode deciding unit.

FIG. 15 offers a block diagram showing the construction of an inventive“inter not coded” mode deciding unit.

FIG. 16 is a block diagram providing the construction of a scalableshape decoding apparatus in the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

In a coding mode for an enhancement layer of an I-picture, e.g., an VOP,a frame, a 16×16 macro block, etc., three modes of “all_(—)0”,“all_(—)255” and “intra not coded” among modes of a conventional systemare represented as only one mode “intra not coded”, the coding mode forthe enhancement layer of the I-picture thus has two modes as thefollowing.

(1) “Intra Not Coded”

(2) “Intra Coded”

First, in case that the coding mode is “intra coded”, in a firstprocess, information for an existence or non-existence of ESD istransmitted. In a second process, then, when the ESD exists, a CAE forall MBs is performed, when the ESD does not exist, the CAE for only TSDis executed.

Next, in case the coding mode is “intra not coded”, there are providedthree following cases.

That is to say, in a first case, there is a case that an MB of the lowerlayer is “all_(—)0” and an MB of the enhancement layer also is“all_(—)0”, or a case that the total number of pixels within one MBhaving a difference from that of an enhancement layer MB is under areference value when the MB of the enhancement layer is “all_(—)0”.

In a second case, there is a case that the MB of the lower layer is“all_(—)255” and the MB of the enhancement layer also is “all_(—)255”,or a case that the total number of pixels within one MB having adifference from that of the enhancement layer MB is under a referencevalue when the MB of the enhancement layer is “all_(—)255”.

In a third case, there is presented a case that the total number ofpixels within one MB having a difference from that of the enhancementlayer MB is under a reference value, when a prediction from an MB of thelower layer is executed in case that the MB of the lower layer is not“all_(—)0” and “all_(—)255”.

Accordingly, in decoding, additional information indicating “intra notcoded” is received, and referring to the lower layer, if the lower layeris “all_(—)0”, all MBs of the enhancement layer are filled with “0s”. Ifthe lower layer is “all_(—)255”, all MBs of the enhancement layer arefilled with “255s”. If the lower layer is not “all_(—)0” or“all_(—)255”, an up-sampling from the MB of lower layer is done tothereby form the MB of the enhancement layer.

FIG. 5 illustrates a flow char providing a method for coding anenhancement layer of an I-picture in the present invention.

In a step ST501, it is detected whether or not a current MB is “intranot coded”. Since the “intra not coded” mode includes three modes of“all_(—)0”, “all_(—)255” and “intra predicted” in the present invention,it is detected by a process provided in FIG. 6 whether the current MB isthe “intra not coded” mode.

In case the current MB is not the “intra not coded” mode, in a stepST502, additional information representing an “intra coded” mode istransmitted to a decoding apparatus, and the current MB is coded by ascan interleaving method and then transmitted to the decoding apparatus.That is, information for an existence or non-existence of ESD istransmitted, and if the ESD exists, the CAE for all MBs is performed,and if the ESD does not exist, the CAE for only TSD is executed.

In case the current MB is the “intra not coded” mode, in a step ST503,additional information representing an “intra not coded” mode istransmitted to the decoding apparatus.

Since the “intra not coded” mode corresponds to the “all_(—)0”,“all_(—)255”, “intra predicted” and “intra not coded” modes in thepresent invention, it is detected whether it belongs to such three casesas shown in FIG. 6. FIG. 6 is a flow chart showing a method fordetecting whether or not the enhancement layer in the invention is the“intra not coded” mode.

In a step ST601, it is detected whether a domain of the lower layercorresponding to the current MB is the “all_(—)0” mode. Since the lowerlayer is obtained by down-sampling a layer that the current MB exists,the domain of the lower layer belonging to the current MB is smallerthan a macro block. If the domain of lower layer is the “all_(—)0” mode,in a step ST602, it is detected whether the current MB is the “all_(—)0”mode. If the current MB and a domain of its corresponding lower layerare the “all_(—)0” mode simultaneously, the additional informationrepresenting the “intra not coded” mode is transmitted to the decoder.

In case the current MB or the domain of its corresponding lower layer isnot the “all_(—)0” mode, in a step ST603, it is detected whether thedomain of the lower layer corresponding to the current MB is the“all_(—)255” mode. In case the domain of lower layer is the “all_(—)255”mode, in a step ST504, it is detected whether the current MB is the“all_(—)255” mode. In case the current MB and the domain of itscorresponding lower layer are the “all_(—)255” mode simultaneously, theadditional information representing the “intra not coded” mode istransmitted to the decoder. In case the current MB or the domain of itscorresponding lower layer is not the “all_(—)255” mode, in a step ST605,it is detected whether the current MB is the “intra predicted” mode. Incase the current MB is the “intra predicted” mode, it is progressed astep for transmitting additional information indicating the “intra notcoded” mode to the decoder. In case the current MB is not the “intrapredicted” mode, it is progressed a step for coding the “intra code” or“inter coded” mode.

As shown in FIGS. 7 and 8, a decoding reception terminal executes adecoding from the “intra not coded” mode and separates the “all_(—)0”and “all_(—)255” modes from the “intra not coded” mode, and thenexecutes corresponding operations respectively. If the mode informationdecoded in a bitstream is the “intra not coded” mode, a decoding shownin FIG. 7 is progressed.

In a step ST701, in case that an MB of the lower layer is “all_(—)0” orall pixels as a sample within a domain of the lower layer correspondingto the current layer MB are ‘0’, the MB of the current layer belongs to“all_(—)0” and in a step ST702 all pixels within the MB of the currentlayer are substituted with ‘0’s

In a step ST703, in case that the MB of the lower layer is “all_(—)255”or all pixels within the domain of the lower layer corresponding to thecurrent layer MB have the values ‘255s’, the MB of the current layerbelongs to “all_(—)255” and in a step ST704 all pixels within the MB ofthe current layer are substituted with ‘255s’.

If the MB of the lower layer is not “all_(—)0” and “all_(—)255”, it is acase that pixels having ‘0’ and ‘255’ exist together within the domainof the lower layer corresponding to the current layer MB. Such a casecorresponds to “intra not coded” having the same meaning in the existingmethod. In this case, in a step ST705, an MB obtained through anexecution of a prediction from the lower layer is used as an MB of thecurrent layer.

The mode of the enhancement layer on the P-picture and B-picture in aconventional system is made up of eight modes, but in the coding methodbased on the present invention, three modes, namely the “all_(—)0”,“all_(—)255” and “intra not coded” modes, are coded as the “intra notcoded” mode, to be then transmitted to the decoding apparatus. Suchmethod is equal to a method in the enhancement layer of the I-picture.

A complication for searching for a motion vector is reduced by nottransmitting the motion vector in the invention. Therefore, theconventional “inter coded && MVD=0” and “inter coded && MVD!=0” arerepresented as “inter coded”, and the conventional “inter not coded &&MVD=0” and “inter not coded && MVD!=0” are represented as “inter notcoded”. As its result, the coding mode for the enhancement layer ofP-picture or B-picture has four modes as follows.

(1) “Intra not coded” (“all_(—)0”, “all_(—)255”, “intra not coded”)

(2) “Intra coded”

(3) “Inter not coded” (“Inter not coded && MVD=0”, “Inter not coded &&MVD!=0”)

(4) “Inter coded” (“Inter coded && MVD=0”, “Inter coded && MVD!=0”)

In case the coding mode is the “intra not coded” and “intra coded”, ithas the same meaning as “intra not coded” and “intra coded” of theenhancement layer on an I-VOP.

In case the coding mode is “inter coded” and “inter not coded”, a motionvector is needed in order to bring the macro block by compensating amotion from a previous VOP. The motion vector is used by adjusting amotion vector of the base layer to a rate of a VOP size.

For a motion vector of “inter not coded”, a motion vector of the baselayer is used as it is. In case the base layer is “MVDs==0 && No Update”or “MVDs!=0 && No Update”, the motion vector is ‘0’. The “inter notcoded” mode means that an MB brought from the previous VOP is comparedwith the current MB by using the motion vector of the lower layer, andthat the sum of pixels within the MB, having a difference by acomparison result, is under a reference value. Thus, in case the codingmode is the “inter not coded” mode, the MB is brought from the previousVOP by utilizing the motion vector of the lower layer, and an additionalcoding or decoding is not done.

For a motion vector of “inter coded”, a motion vector of the base layeris used as it is. In case the base layer is “MVDs==0 && No Update” or“MVDs!=0 && No Update”, the motion vector is ‘0’. The “inter coded” modemeans that an MB brought from the previous VOP is compared with thecurrent MB by using the motion vector of the lower layer, and that thesum of pixels within the MB, having a difference by a comparison result,is more than the reference value. Thus, in case the coding mode is the“inter coded” mode, the CAE is performed by using the MB brought fromthe previous VOP through a use of the motion vector of the lower layer,to thereby gain an MB of the enhancement layer.

In the present invention, the mode number of enhancement layer for theP-picture and B-picture is reduced from 8 modes in the existing systemto 4 modes.

FIG. 9 offers a flow chart provided for the sake of coding the P-pictureand B-picture of enhancement layer in the present invention. In a stepST901, it is detected by the method described through FIG. 6 whether thecurrent MB is “intra not coded”. When the current MB is the “intra notcoded” mode, the coding is not done, and in a step ST902, onlyadditional information showing the “intra not coded” mode istransmitted. When the current MB is not the “intra not coded” mode, themotion vector of the base layer is adjusted to a rate of an image sizeand used, for motion vectors of “inter not coded”, “inter coded” and“inter not coded”, to thereby regenerate the motion vector in a stepST903. In a step ST904, it is detected whether the current. MB is the“inter not coded” mode. In case the current MB is “inter not coded”, thecurrent MB is not coded but only additional information indicating“inter not coded” is transmitted, in a step ST905.

In case the current MB is not “inter not coded”, it is detected in astep ST906 whether the current MB is the “intra coded” mode. In case thecurrent MB is “intra coded”, additional information indicating the“intra coded” mode and data gotten by coding the current MB through thescan interleaving method are transmitted to the decoding apparatus, in astep ST908. In case the current MB is not “intra coded”, in a stepST907, additional information indicating the “inter coded” mode istransmitted and the CAE for the current MB is executed and then the CAEcoded macro block is transmitted to the decoding apparatus.

In case the current MB is the “inter coded” and “inter not coded” modes,the motion vector is needed in order to bring an MB by performing amotion compensation from/on the previous image. The motion vector isused after adjusting a motion vector of the base layer to a rate of animage size.

The following is a method for obtaining a motion vector from the baselayer.

First, in case a mode of a corresponding MB on the base layer is“all_(—)0”, “all_(—)255” or “intraCAE”, a motion vector of an MB on thecurrent layer is ‘0’.

Secondly, in case the mode of corresponding MB on the base layer is“MVDs==0 && No Update”, ““MVDs!=0 && No Update”, “interCAE && MVDs==0”or “interCAE && MVDs!=0”, a motion vector regenerated on the base layeris used.

In such process, the motion vector of the base layer is adjustedaccording to a ratio of an image size of the base layer and the currentlayer. An X axial motion vector is adjusted according to a rate of an Xaxial size on an image and a Y axial motion vector is adjusted accordingto a rate of a Y axial size on the image. For example, referring to FIG.10, if an image of the current layer, 101, is n times larger on an Xaxial than an image of the base layer 102, a motion vector of thecurrent layer, V, equals to n times v, v being a motion vector of thebase layer. Namely it becomes V=n*v. If the image of the current layer,101, is m times larger on a y axial than the image of the base layer102, the motion vector of the current MB is gained by multiplying themotion vector of y axial by m, on the motion vector of the base layer.

FIG. 11 presents a flow chart for decoding P-picture or B-picture of theenhancement layer in the invention. In a step ST110, a mode is decodedfrom a bitstream. In case the current MB is “intra not coded” in a stepST111, a pixel is selected without a decoding according to a mode of acorresponding macro block in a step ST112. In case the current MB is“intra not coded” in a step ST111, a pixel is selected without adecoding according to a block of a corresponding macro block. In casethe current MB is not the “intra not coded” mode, a motion vector of thelower layer is used as it is as afore-mentioned system, for motionvectors of “inter not coded”, “inter coded” and “inter not coded”, tothereby regenerate the motion vector in a step ST113. In a step ST114,it is detected whether the current MB is the “inter not coded” mode. Incase the current MB is “inter not coded”, in a step ST115 the current MBis not coded but a motion compensation is done from a previous image tothus fill pixels of the current MB with. In case the current MB is not“inter not coded”, in a step ST116, it is detected whether the currentMB is the “intra coded” mode. In case the current MB is “intra coded”,the current MB is decoded by a scan interleaving method in a step ST118.If not “intra coded”, the CAE for the current MB is executed in a stepST117.

FIG. 12 furnishes a block diagram showing the construction of aninventive scalable shape coding apparatus. A large number of subsamplingunits 1210, 1211, . . . , 121N−2, 121N−1, receive images from itsprevious subsampling units 1210, 1211, . . . , 121N−2 and perform asubsampling. Numbers of scan order converting units 1220, 1221, . . . ,122N−1, 122N, receive images of respective layers subsampled in thesubsampling units 1210, 1211, . . . , 121N−2, 121N−1, and divide theimages into macro blocks of a given size and then output them. Numerousscalable shape coding units 1230, 1231, . . . , 123N−1, 123N receiveimage macro blocks of the respective layers and image blocks of the baselayer and previous images of the respective layers from the scan orderconverting units 1220, 1221, . . . , 122N−1, 122N, and encode threemodes of “all_(—)0”, “all_(—)255” and “intra not coded” as one mode. Thescalable shape coding units 1230, 1231, . . . , 123N−1, 123N alsoperform a scalable shape coding by encoding “inter not coded && MVD=0”and “inter not coded && MVD!=0” as the “inter not coded” mode and “intercoded && MVD=0” and “inter coded && MVD!=0” as the “inter coded” mode.

The inputted pictures are inputted to the N−1 layer subsampling unit121N−1 and the N layer scan order converting unit 122N. The N layer scanorder converting unit 122N divides an N layer image into macro blocks ofa given size, e.g., macro blocks of 16×16, etc., and then outputs them.These macro blocks are scalably encoded in an N layer scalable shapecoding unit 123N and transmitted by a bitstream to the decodingapparatus. The N layer scalable shape coding unit 123N receives previousimages of an N layer, macro blocks of the N layer image, macro blocks ofan N−1 layer image and motion vectors of a base layer coding unit 1230,and performs a scalable shape coding.

An N−1 layer subsampling unit, 121N−1 layer, subsamples inputted images,converts the images into N−1 layer images, and outputs the convertedimages. For instance, the images are divided into MBs of 2×2, and onepixel per 2×2 MB is extracted therefrom and made to subsampled images.Such subsampled N−1 layer image is divided into MBs of a given size inthe N−1 layer scan order converting unit 122N−1, and inputted to the N−1layer scalable shape coding unit 123N−1. The N−1 layer scalable shapecoding unit 123N−1 receives previous images of an N−1 layer, MBs of N−1layer image, MBs of an N−1 layer image and motion vectors of a baselayer coding unit 1230, and performs a scalable shape coding.

Like the above-mentioned, several subsamplings for the N layer to theN−1 layer, the N−1 layer to the N−2 layer, . . . are done; suchsubsampled image MBs of respective layers and image MBs of its lowerlayer and previous images of the respective layers are inputted tonumerous scalable shape coding units 1230, 1231, . . . , 123N−1, 123N;three modes of “all_(—)0”, “all_(—)255” and “intra not coded” areencoded as one mode of “intra not coded”; “inter not coded && MVD=0” and“inter not coded && MVD!=0” are scalably encoded as the “inter notcoded” mode; and “inter coded && MVD=0” and “inter coded && MVD!=0” arescalably coded as the “inter coded” mode. Therefore, the scalable shapecoding is fulfilled for numerous image layers having resolution of theN+1 number of layers.

FIG. 13 offers a block diagram presenting one embodiment of an inventivescalable shape coding unit. The scalable shape coding units 1230, 1231,. . . , 123N−1, 123N of the respective layers have the same structure,and for the sake of an explanatory convenience, the scalable shapecoding unit of N layer 123N is described.

A motion vector adjusting unit 131 receives a motion vector from thescalable shape coding unit 1230, enlarges the motion vector to a rate ofthe current and base layers, and outputs it. A motion compensating unit132 receives a previous image of the current layer, the N layer, and theadjusted motion vector outputted from the motion vector adjusting unit131, searches for a part corresponding to the current MB from theprevious image of the current layer, and outputs it. A CAE coding unit133 receives MBs of the current layer image and the motion compensatedprevious image of the current layer and performs a CAE coding. A scaninterleaving coding unit 134 receives MBs of the current layer image andthe lower layer (N−1 layer) image and executes a coding through the scaninterleaving method. An “intra not coded” mode deciding unit 135receives MBs of the current layer image and the lower layer image andoutputs a signal indicating whether or not the MB is the “intra notcoded” mode. An “inter not coded” mode deciding unit 136 receives MBs ofthe current layer image and the motion compensated previous image of thecurrent layer outputted from the motion compensating unit 132 andoutputs a signal indicating whether or not the current MB is the “internot coded” mode. A comparison unit 137 compares sizes of bitstreamoutputted from the scan interleaving coding unit 134 and the CAE codingunit 133 and outputs a signal for selecting the smaller bitstream. Amode table storing unit 138 receives signals from the “intra not coded”mode deciding unit 135, the “inter not coded” mode deciding unit 136 andthe comparison unit 137 and outputs data corresponding to a modeselected by a compound of the signals. A selection unit 139 receives the“intra not coded” mode deciding signal, the “inter not coded” modedeciding signal and a comparison result signal of the comparison unit137, and selects and outputs one of signals outputted from the scaninterleaving coding unit 134 and the CAE coding unit 133.

The “intra not coded” mode deciding unit 135 receives MBs of the currentlayer image and the lower layer image, the current layer being, e.g., anN layer, and the lower layer being, e.g., an N−1 layer. The “intra notcoded” mode deciding unit 135 also decides whether the MB of currentlayer image is the “intra not coded” mode and outputs its result signal,referring to FIG. 6.

FIG. 14 shows a block diagram providing the construction of an inventive“intra not coded” mode deciding unit. An object/background non-codedeciding unit 141 carries out an up-sampling for a macro block of thelower layer corresponding to the current MB, and extracts a differenceabsolute value between the up-sampled MB and the current MB, and detectswhether its difference is less than a threshold value. A lower layerobject mode deciding unit 142 receives a macro block of the lower layercorresponding to the current MB and detects whether it is an objectmode. A lower layer background mode deciding unit 143 receives an MB ofthe lower layer corresponding to the current MB and detects whether itis a background mode. A current layer object mode deciding unit 144receives the current MB and detects whether it is the background mode. Acurrent layer background error deciding unit 145 receives the current MBand detects whether it is the object mode. A logical operation unit 146executes a logical operation for signals outputted from theobject/background non-code deciding unit 141, the lower layer objectmode deciding unit 142, the lower layer background mode deciding unit143, the current layer object mode deciding unit 144 and the currentlayer background error deciding unit 145, and outputs a signalrepresenting whether any one mode of “all_(—)0”, “all_(—)255” and “intrapredicted” is generated.

The object/background non-code deciding unit 141 includes an up-samplingsector 141 a for up-sampling the MB of the lower layer corresponding tothe current MB, a difference absolute value extracting sector 141 b forextracting the difference absolute value between the up-sampled MB ofthe lower layer and the current MB and an error comparing sector 141 cfor detecting whether the extracted difference absolute value is lessthan the threshold value.

The up-sampling sector 141 a converts the MB of the lower layercorresponding to the current MB into an MB having the same size as thecurrent MB by using an interpolation regulation for repeatinghorizontally and vertically. A differential value between pixels of theup-sampled lower layer MB and the current MB is calculated in thedifference absolute value extracting sector 141 b and its differentialvalue is applied to an absolute value, wherein the pixels thereofrespectively correspond to them of the current MB. In such a process,each of the pixels of the current MB and the up-sampled lower layer MBhas a value of ‘0’ or ‘255’ and the current MB, thus the absolute valuefor the differential value also has a value of ‘0’ or ‘255’. That is,since the value of ‘255’ is presented in only case that mutuallydifferent values are subtracted, a pixel of a position having the valueof ‘255’ represents that the current MB is different from the up-sampledlower layer MB.

The macro block made up of such difference absolute values is inputtedto the error comparing sector 141 c, to thereby check whether an erroris under a reference value. In other words, the macro block constructedwith the difference absolute values is divided into MBs of 4×4 size, andthe error is detected as the value under the reference value when theerror value of all macro blocks is less than the threshold value or sameas. When the error is under the reference value, it becomes the “intrapredicted” mode and the error comparing sector 141 c outputs ‘1’.

The lower layer object mode deciding unit 142 includes an objectdeciding sector 142 a for checking whether all images of the lower layercorresponding to the current macro block have an object value, e.g.,‘255’,outputting ‘1’ in case all is the object value, and outputting ‘0’in case all is not the object value; and an OR gate 142 b for executingan OR operation for outputs from the object deciding sector 142 a and amode of MB on the previous image of the lower layer.

The lower layer MB corresponding to the current MB is inputted to thelower layer object mode deciding unit 142 if all pixels constituting thelower layer MB corresponding to the current MB have ‘255s’ of the objectvalues, ‘1’ is outputted to represent the “all_(—)255” mode. If not, a‘0’ signal is outputted. When even one of a mode of MB on the previousimage of the lower layer and the object deciding sector 142 a outputs‘1’, that is, if all pixels of the lower layer macro block correspondingto the current MB have the value of ‘255’,or even though there existpixels which do not have the value of ‘255’, if their values representthe “all_(—)255” mode as values less than the threshold value, the ORgate 142 b outputs ‘1’.

The lower layer background mode deciding unit 143 includes; a backgrounddeciding sector 143 a for detecting whether or not all pixelsconstituting the lower layer MB belonging to the current MB have ‘0s’ asa background value; and an OR gate 143 b for performing the OR operationon a mode of MB on the previous image of the lower layer and thebackground deciding sector 143 a.

The lower layer MB corresponding to the current MB is inputted to thelower layer object made deciding unit 142. The background decidingsector 143 a outputs ‘1’ if all pixels on the lower layer domainbelonging to the macro block of the current layer are ‘0s’. If not, thebackground deciding sector 143 a outputs ‘0’. The OR gate 143 c outputs‘1’ when even any one out of a mode of MB on the previous image of thelower layer and the background deciding sector 143 a outputs ‘1’. Thatis to say, if the lower layer MB corresponding to the current MB is the“all_(—)0” mode, the OR gate 143 c outputs ‘1’,the “all_(—)0” mode beinga case that all pixels are ‘0s’ or values of pixels not ‘0’” are underthe threshold value.

The current layer object mode deciding unit 144 is made up of an objectdifference absolute value extracting sector 144 a for obtainingdifferential values between inputted current MBs and MBs all having avalue of ‘0’ and taking their absolute values; and an error comparingsector 144 b for detecting whether or not the extracted differenceabsolute value is under the threshold value.

The current MBs are inputted to the current layer object mode decidingunit 144, and MB all having a value of ‘0’ and an absolute value on adifferential value are taken thereto. In the error comparing sector 144b, it is detected whether such difference absolute value is less thanthe threshold value. If less than the threshold value, the current MBbecomes the “all_(—)255” mode and the error comparing sector 144 boutputs ‘1’.

The current layer background error comparing unit 145 receives thecurrent MB and divides the current MB into blocks of 4×4 and detectsthat the error is under the reference value when the error of the MBs isless than the threshold value, 16×alpha, or same as. In case it isdetected that the error is under the reference value, the errorcomparing sector 145 outputs ‘1’, to thereby represent that the currentMB is the “all_(—)0” mode.

When the lower layer object mode deciding unit 142 and the current layerobject deciding unit 144 output ‘1’ simultaneously, an AND gate U1outputs ‘1’. That is, when the current layer MB and its correspondinglower layer MB have an object value together, the AND gate U1 outputs‘1’. Likewise, when the lower layer background mode deciding unit 143and the current layer background mode deciding unit 145 output ‘1’ atthe same time, an AND gate U2 outputs ‘1’. That is to say, the currentlayer MB and its corresponding lower layer MB have a background valuetogether, the AND gate U2 outputs ‘1’. Thus, if even any one out of“all_(—)0”, “all_(—)255” and “intra predicted” corresponds thereto, anAND gate U4 outputs ‘1’. It thus means that any one among “all_(—)0”,“all_(—)255” and “intra predicted” was generated.

FIG. 15 shows a block diagram presenting the construction of aninventive “inter not coded” mode deciding unit. The “inter not coded”mode deciding unit includes a difference absolute value extracting 151for receiving the current MB and a corresponding MB of a motioncompensated previous image and taking its difference absolute value; anerror comparing unit 152 for detecting whether the difference absolutevalue is less than the threshold value; and an AND gate 153 forperforming an AND operation on information I/P, B, wherein theinformation is about that an output from the error comparing unit 152and the currently inputted image are an intra mode I and a predictedmode P or a both direction predicted mode B.

The difference absolute value extracting unit 151 receives the currentMB and a corresponding MB of a motion compensated previous image andthen takes its difference absolute value, after that, only pixels ofpositions having values different from one another have a value of‘255’. The error comparing unit 152 detects whether the differenceabsolute value is less than the threshold value. When the current imageis the intra mode, the I/P and B signals have a value of ‘0’. Thus, theAND gate 153 outputs a comparison result of the error comparing unit 152in only case that the current image is the predicted mode P or the bothdirection predicted mode B.

FIG. 16 gives a block diagram showing the construction of an inventivescalable shape decoding apparatus.

In the scalable shape decoding apparatus, the N+1 number of layers arepresented so as to be compared with the scalable shape coding apparatusshown in FIG. 12. A large number of scalable shape decoding units 1610,1611, . . . , 161N−1, 161N respectively receive bitstreams of respectivelayers, a motion vector of base layer, previous images and decodingimages, to perform a scalable shape decoding. An image storing unit 162stores image MBs of a current layer outputted from the N layer scalableshape coding unit 161N.

FIG. 17 sets forth a block diagram providing the construction of aninventive scalable shape decoding unit.

Scalable shape decoding units on respective layers, 1610, 1611, . . . ,161N−1, 161N have the same structure as one another and the scalableshape decoding unit 161N of an N layer is described for the sake of anexplanatory convenience.

A motion vector adjusting unit 171 receives a motion vector from thebase layer scalable shape decoding unit 1610, enlarges the motion vectorby a rate of the current and base layers, and outputs it. A motioncompensating unit 172 receives a previous image of the current layer,the N layer, and the adjusted motion vector outputted from the motionvector adjusting unit 171, compensates a motion for a macro block Bcorresponding to the current MB from the previous image of the currentlayer, and outputs it. A mode decoding unit 173 receives current layerbitstreams and the I/P and B signals and decodes mode information. An“intra not coded” MB constructing unit 174 receives MBs of a lower layerimage and their modes, and processes them according to a regulationdecided previously and outputs current image MBs A. A CAE coding unit176 receives bitstreams of the current layer image and motioncompensated previous image of the current layer, and outputs signals Dexecuted in a CAE coding. A scan interleaving decoding unit 175 receivesthe bitstreams of the current layer image and MBs of the lower layer(N−1 layer) image, and outputs signals C decoded by a scan interleavingmethod. A multiplex unit 177 outputs one out of A, B, C and D accordingto a mode decoded in the mode decoding unit 173.

FIG. 18 is a block diagram showing the construction of the “intra notcoded” MB constructing unit in the scalable shape decoding unit inaccordance with the present invention. An object mode deciding unit 181outputs ‘1’ when all pixels constituting the lower layer MBcorresponding to the current MB have ‘255s’. If not, the object modedeciding unit 181 outputs ‘0’. In case a mode of the lower layer MB is“all_(—)255” or an output of the object mode deciding unit 181 is ‘1’,anoutput of the OR gate U1 is ‘1’. In a background mode deciding unit 182,all pixels within an area corresponding to the current layer MB, amongpixels within a lower layer MB, have a value of ‘0’, a value of ‘1’ isoutputted, if not, a value of ‘0’ is outputted. In case that a mode ofthe lower layer MB is “all_(—)0” or an output of the background modedeciding unit 182 is ‘1’, an output of an OR gate U2 is ‘1’. An“all_(—)0” block generating unit 183 generates MBs in which all pixelshave a value of ‘0’. An “all_(—)255” block generating unit 184 generatesMBs in which all pixels have a value of ‘255’. An up-sampling unit 185up-samples a domain of the lower layer to construct a current MB. Afirst multiplexer 186 selects an output from the “all_(—)255” blockgenerating unit 184 or the up-sampling unit 185 in response to an outputsignal of the OR gate U1. A second multiplexer 187 selects an outputfrom the “all_(—)0” block generating unit 183 or the first multiplexer186 in response to an output signal of the OR gate U2.

In the object mode deciding unit 181, if all pixels within an areacorresponding to the current layer MB, among pixels within a lower layerMB, have a value of ‘255’, ‘1’ is outputted, and if not, ‘0’ isoutputted. If a mode of the lower layer MB is “all_(—)255” or an outputof the object mode deciding unit 181 is ‘1’, an output of the OR gate U1is ‘1’. Such “all_(—)0” and “all_(—)255” modes are not used fortransmitting, coding and decoding but they are used by storing outputsfrom the OR gates U1, U2 at every MB by the “all_(—)0” and “all_(—)255”modes.

In the background mode deciding unit 182, all pixels within an areacorresponding to the current layer MB among pixels within a lower layerMB have a value of ‘0’, a value of ‘1’ is outputted, if not, a value of‘0’ is outputted. In case that a mode of the lower layer MB is“all_(—)0” or an output of the background mode deciding unit 182 is ‘1’,an output of the OR gate U2 is ‘1’. The “all_(—)0”block generating unit183 generates MBs in which all pixels have a value of ‘0’, and allpixels of an outputted MB have a value of ‘0’. The “all_(—)255” blockgenerating unit 184 constructs MBs in which all pixels have a value of‘2550’, and all pixels of an outputted MB have a value of ‘255’.

The up-sampling unit 185 up-samples a domain of the lower layer tothereby construct a current MB. If an output “all_(—)255” of the OR gateU1 is ‘1’, the first MUX 186 selects, as its own output, an output ofthe “all_(—)255” block generating unit 184, namely the MBs in which allpixels have a value of ‘255’. If ‘0’, an output of the up-sampling unit185, namely an up-sampled MB, is selected. If an output “all_(—)0” ofthe OR gate U2 is ‘1’, the second MUX 187 selects an output of the“all_(—)0” block generating unit 183 as its own output, namely the MBsin which all pixels have a value of ‘0’. If ‘0’, an output of the firstMUX 186 is selected.

In coding an image to multiple of layers, there is a high correlationbetween an enhancement layer and its down sampled lower layer. In otherwords, if the enhancement layer is the “intra not coded” mode, there isa high probability for that its lower layer may be also the “intra notcoded” mode. What bits for a coding mode of enhancement layer on anI-picture and P-picture, or B-picture, are assigned by considering suchcorrelation, is the method capable of lessening the quantity of codingbits. The following describes a bit assigning method for a coding modeof the enhancement layer on the I-picture and P-picture(B-picture).

When the lower layer coding mode is known, a generating bit number forthe coding mode of enhancement layer is assigned with the small quantityby using Huffman coding system, if a generating probability is high, andif the generating probability is low, a long bitstream is assigned. Forexample, in case the lower layer is the “intra not coded” mode, aprobability that the current layer may be the “intra not coded” mode ishighest, thus bits on the shortest length are assigned, and then 2,3, .. . bits are assigned to a coding mode having a high generativeprobability. Since the “intra coded” modes are most generated in acoding mode of MB, most of “intra coded” modes receive bits of relativesmall quantity as 1 bit or 2 bits regardless all coding modes.

An example through an inventive coding bit assigning method is presentedas follows.

Enhancement Layer Mode (1) (2) (3) (4) lower layer (1) 1 2 3 3 mode (2)2 1 3 3 (3) 3 2 1 3 (4) 3 1 3 2

The following provides an embodiment for the enhancement layer mode,when the lower layer mode is known through the above-mentioned method.Two codes for each assigned bit of each enhancement layer is herewithused as follows.

(1) 1 bit: 0, 2 bit: 10, 3 bit: 110, another 3 bit: 111

(2) 1 bit: 1, 2 bit: 01, 3 bit: 001, another 3 bit: 000

The following describes an additional information constructing methodand a code table of the present invention on an enhancement layer of theI-picture and P-picture, and B-picture.

In an enhancement layer of the I-picture, two kinds of modes as thefollowing are used.

(1) “intra not coded”

(2) “intra coded”

In the conventional method, on an enhancement layer of the I-picture,three kinds of modes are used, namely, “all_(—)0”, “all_(—)255” and“intra coded”. In the present invention, the “all_(—)0” and “all_(—)255”modes in the existing system and the “intra not coded” mode on theenhancement layer of P-picture and B-picture in the existing system aretransmitted by one mode “intra not coded”. A receiving terminal detectsby using information of the lower layer whether or not the received“intra not coded” mode is “all_(—)0”or “all_(—)255”. Accordingly, onlytwo modes are used in the present invention, in comparison with theconventional method using three modes, thereby resulting in reducing thequantity of bits required for transmitting modes.

Codes of modes for respective MBs are encoded by using a code table suchas the following table. Each mode has a fixed length and 1 bit for it istransmitted.

Shape Mode Code “intra not coded” 1 “intra coded” 0

In an MPEG-4 the standardization of which is presently under aprogression on the ISO/IEC WG11, in order to discriminate an image froma bitstream, twenty-three consecutive ‘0s’ within the image arerepresented when an image starts to. In case 23 consecutive ‘0s’ aregenerated within the image, it is decided as the beginning of the image.In case it is not the beginning of the image, it is thus necessary notto generate 23 consecutive ‘0s’. It is profitable to generate many ‘1s’as possible so that 23 consecutive ‘0s’ may not be easily generated, 23consecutive ‘0s’ being available to be easily generated by a case thatsome ‘1s’ out of ‘1s’ can be changed to ‘0s’ owing to a transmissionerror. Accordingly, the code table is changed as follows so that thecode table shown in the above may include ‘1’ on the mode of “intracoded”.

Shape Mode Code “intra not coded” 1 “intra coded” 01

A first method for coding the lower layer of P-picture is as follows.

(1) “all_(—)0” or “all_(—)255” or “intra not coded”

(2) “intraCAE” or “intra coded”

(3) “MVDs==0 && No Update” or “MVDs!=0 && No Update” or “inter notcoded”

(4) “interCAE && MVDs==0” or “interCAE && MVDs!=0” or “inter coded”

Coding modes of an enhancement layer on the P-picture are as follows.

(1) “Intra Not Coded”

(2) “Intra Coded”

(3) “Inter Not Coded”

(4) “Inter Coded”

In a case of the enhancement layer of the P-picture and B-picture, fourkinds of modes are used as follows.

(1) “intra not coded”

(2) “intra coded”

(3) “inter not coded”

(4) “inter coded”

In the conventional system, a mode of the enhancement layer on theP-picture and B-picture is constructed by eight modes. In the presentinvention, three modes as the “all_(—)0”, “all_(—)255” and “intra notcoded” modes become one mode as the “intra not coded” mode, to be thentransmitted to the decoding apparatus. Such method is equal to a methodin a mode for the enhancement layer of the I-picture. A complication forsearching for a motion vector is reduced by not transmitting the motionvector in the present invention. Therefore, the conventional “intercoded && MVD=0” and “inter coded && MVD!=0” modes are represented as onemode “inter coded”, and the conventional “inter not coded && MVD=0” and“inter not coded && MVD!=0” modes are represented as one mode “inter notcoded”. In case the coding mode is “inter coded” and “inter not coded”,a motion vector is needed in order to bring the macro block bycompensating a motion from a previous image. The motion vector is usedafter adjusting a motion vector of the base layer to a rate of an imagesize.

A method for getting the motion vector from the base layer is asfollows.

First, in case a mode of a corresponding MB on the base layer is“all_(—)0”, “all_(—)255” or “intraCAE”, a motion vector of an MB on thecurrent layer is ‘0’.

Secondly, in case the mode of corresponding MB on the base layer is“MVDs==0 && No Update”, ““MVDs!=0 && No Update”, “interCAE && MVDs==0”or “interCAE && MVDs!=0”, a motion vector regenerated on the base layeris used.

In such process, the motion vector of the base layer is adjustedaccording to a ratio of an image size of the base layer and the currentlayer. An X axial motion vector is adjusted according to a rate of an Xaxial size on an image and a Y axial motion vector is adjusted accordingto a rate of a Y axial size on the image. For instance, if an image ofthe current layer is n times on the X axial and m times on the y axial,larger than an image of the base layer, the motion vector of the currentMB is obtained by multiplying the motion vector of X axial by n andmultiplying the motion vector of Y axial by m, on the motion vector ofthe base layer.

In accordance with the present invention, modes for the enhancementlayer of the P-picture and B-picture are reduced from eight modes in theconventional system to four modes. Codes of modes for respective MBs areencoded by using coding tables such as the following tables. In order tolessen bits generated at this time, the coding table is constructed byusing pixels values and a mode of the lower layer.

A second method for coding a mode of a just lower layer is as follows.There are cases that,

(1) “all_(—)0”, “all_(—)255”, “intra not coded” or all pixels (sample)within the lower layer MB area corresponding to the current layer MB are‘0’ or ‘2550’,

(2) “intraCAE” or “intra coded”,

(3) “MVDs==0 && no update”, “MVDs!=O && no update” or “inter not coded”,and

(4) “interCAE && MVDs==0”, “interCAE && MVDs!=0”.

Or, there are cases that a just lower layer of “inter coded”, namely alower layer, is the base layer or is not the base layer. Such each casesmay be respectively explained as follows.

First, the following is for a case that the lower layer is the baselayer.

(1) “all_(—)0” or “all_(—)255” or all pixels (sample) within the lowerlayer MB area corresponding to the current layer MB are ‘0’ or ‘255’

(2) “intraCAE”

(3) “MVDs==0 && no update” or “MVDS!=0 && no update”

(4) “interCAE && MVDs==0” or “interCAE && MVDs!=0”.

Next, the following is for a case that the lower layer is not the baselayer.

(1) “intra not coded” or all pixels (sample) within the lower layer MBarea corresponding to the current layer MB are ‘0’ or ‘255’

(2) “intra coded”,

(3) “inter not coded”

(4) “inter coded”

The code, first shape code, for a mode of an enhancement layer isdecided as follows, when all lower bases are known.

CODE TABLE 1 Enhancement Layer Mode (1) (2) (3) (4) lower (1) 0 10 110111 layer (2) 110 0 10 111 mode (3) 110 10 0 111 (4) 111 0 111 10

In the MPEG-4 the standardization of which is presently under aprogression on the ISO/IEC WG11, in order to discriminate an image froma bitstream, twenty-three consecutive ‘0s’ within the image arerepresented when an image starts to. In case 23 consecutive ‘0s’ aregenerated within the image, it is decided as the beginning of the image.In case it is not the beginning of the image, it is thus necessary notto generate 23 consecutive ‘0s’. Since there may be generated 23consecutive ‘0s’ in the <code table 1>, the table such as the followingis used.

CODE TABLE 2 Enhancement Layer Mode (1) (2) (3) (4) lower (1) 1 01 001000 layer (2) 110 0 10 111 mode (3) 001 01 1 000 (4) 110 0 111 10

A case of (3) can occur more frequently in a case that the just lowerlayer, lower layer, is (2) than in a case that the current layer,enhancement layer, is (1). In this case, the following table is used.

CODE TABLE 3 Enhancement Layer Mode (1) (2) (3) (4) lower (1) 1 01 001000 layer (2) 10 0 110 111 mode (3) 001 01 1 000 (4) 110 0 111 10

It is profitable to generate many ‘1s’ as possible so that 23consecutive ‘0s’ may not be easily generated, 23 consecutive ‘0s’ beingavailable to be easily generated by a case that some ‘1s’ out of ‘1s’can be changed to ‘0s’ owing to a transmission error. Accordingly, thecode table is changed as follows so that the code table shown in theabove may include ‘1’ for all modes. The table such as the following isconstructed by correcting the <code table 2>.

CODE TABLE 4 Enhancement Layer Mode (1) (2) (3) (4) lower (1) 1 01 0010001 layer (2) 001 1 01 0001 mode (3) 001 01 1 0001 (4) 001 1 0001 01

For the same reason as the above, the table such as the following isalso constructed by correcting the <code table 3>.

CODE TABLE 5 Enhancement Layer Mode (1) (2) (3) (4) lower (1) 1 01 001000 layer (2) 10 0 110 111 mode (3) 001 01 1 000 (4) 110 0 111 10

In the present invention, an order for deciding the mode is gained asfollows by improving a conventional method. That is, in order to searchfor a desired image or a binary image promptly, there is a necessity todiscriminate MBs of “all_(—)0” or “all_(—)255” from MBs which do nothave “all_(—)0” or “all_(—)255”, namely the MBs corresponding to anedge. Such a discrimination can make a binary image of a small size,which is capable of representing the MB with one pixel, and an overallimage can be almost detected from the binary image of small size, andalso it can be checked whether or not the binary image is the imagerequired from the overall image. Namely, the MB of “all_(—)0” isrepresented by pixels having a value of ‘0’, and the MB of “all_(—)255”is represented by pixels having a value of ‘255’. The MB which is not“all_(—)0” or “all_(—)255”, namely MB corresponding to an edge, isrepresented with a value of ‘128’ to thereby get an image of a smallsize. Like this, in order to definitely discriminate between the MBswhich are “all_(—)0” or “all_(—)255”, or are not “all_(—)0” or“all_(—)255”, “all_(—)0” or “all_(—)255” are first decided. Thus, themode is decided by the following described order.

It is decided by the following order on the base layer.

(1) “all_(—)0” or “all_(—)255”

(2) “MVDs==0 && no update” or “MVDs!=0 && no update”

(3) A mode which has a small generating quantity of bits, among“intraCAE” and “interCAE && MVDs==0” or “interCAE && MVDs!=0”.

A mode deciding method for the I-picture and P-picture of theenhancement layer is used as follows, since what the “all_(—)0” or“all_(—)255” mode is first decided on the enhancement layer makes thequantity of generating bits small, with the above-mentioned reason.

The mode deciding method for the enhancement layer of I-picture is asfollows.

(1) In a case of “all_(—)0” or “all_(—)255”, a decision as “intra notcoded”

(2) An Mb predicted from the lower layer and a current MB are compared,and in case its error is under a reference value, a decision as “intranot coded”

(3) “intra coded”

The mode decision order for the enhancement layer of P-picture orB-picture is progressed by the order presented in FIG. 9, and what“inter not coded” is decided earlier than “intra predicted” makes ageneration of bits small. The following mode decision order is gotten byconsidering such points.

(1) In a case of “all_(—)0” or “all_(—)255”, a decision as “intra notcoded”

(2) a decision of “intra not coded”

What is claimed is:
 1. A method for coding a scalable shape binary imageby using a coding mode of an enhancement layer, wherein the scalableshape binary image has at least one enhancement layer including anenhanced resolution than that of a lower layer, said method comprisingthe steps of: a) dividing an image of an enhancement layer into blockshaving a predetermined size; b) comparing pixels in each block of theenhancement layer with its corresponding pixels within an area of thelower layer, and determining a coding mode of each block of theenhancement layer based on the comparison result, wherein the codingmode is one of (0) “intra not coded” mode, (1) “intra coded” mode, (2)“inter not coded” mode and (3) “inter coded” mode; c) if the coding modefor P-VOP in the enhancement layer is one of “intra not coded” mode and“intra coded” mode, transmitting additional information representing itscoding mode; and d) if the coding mode for B-VOP in the enhancementlayer is one of “intra not coded” mode, “intra coded” mode, “inter notcoded” mode and “inter coded” mode, transmitting the additionalinformation indicating its coding mode.
 2. The method as recited inclaim 1, wherein “intra not coded” mode means that the number of pixelsin each enhancement layer block different from pixels of the lower layeris less than a reference value, in the case of “intra not coded” mode,the enhancement layer block is not encoded, wherein in case of “intracoded” mode, the enhancement layer block is encoded, wherein “inter notcoded” mode and “inter coded” mode, no motion vector is encoded forprediction of the enhancement layer block and the motion vector ofblocks of the lower layer is utilized, wherein “inter not coded” modemeans that the number of pixels in each enhancement layer blockpredicted from a previous video object plane (VOP) different from pixelsof a current VOP is less than a reference value, and in the case of“inter not coded” mode, a current block of the enhancement layer blockis not encoded, and wherein in case of “inter coded” mode, the currentblock of the enhancement layer is encoded.
 3. The method as recited inclaim 1, wherein the step c) includes the step of: if the coding mode is“intra coded ” mode, coding the enhancement layer to generate a firstcoded data and transmitting the additional information indicating “intracoded” mode and the first coded data, wherein the first coded data isgenerated based on a intra mode CAE (context-based encoding) method; andwherein the step d) includes the step of: if the coding mode is “intercoded” mode, coding the enhancement layer to generate a second codeddata and transmitting the additional information indicating “intercoded” mode and the second coded data, wherein the second coded data isgenerated based on a inter mode CAE method.
 4. The method as recited inclaim 1, wherein the additional information for B-VOP in the enhancementlayer has a value described in a table as: Enhancement Layer Mode (0)(1) (2) (3) Lower (0) 1 01 001 000 Layer (1) 110 0 10 111 Mode (2) 00101 1 000 (3) 110 0 111
 10.


5. The method as recited in claim 4, wherein the coding modes (0), (1),(2), and (3) of the lower layer, in case they are the coding modes ofthe base layer, are respectively mapped as follows: (0) all_(—)0 orall_(—)255 (1) intraCAE (2) MVDs==0 && No Update or MVDs!=0 && No Update(3) interCAE && MVDS==0 or interCAE && MVDS!=0.
 6. The method as recitedin claim 1, wherein the additional information for P-VOP in theenhancement layer has a value described in a table as: Coding mode Code“intra not coded” 1 “intra coded” 01


7. A method for decoding a scalable shape binary image by using a codingmode of an enhancement layer, wherein the scalable shape binary imagehas at least one enhancement layer including an enhanced resolution thanthat of a lower layer, said method comprising the steps of: a) receivingadditional information indicating a coding mode of the enhancement layerand determining the coding mode, wherein the coding mode is one of (0)“intra not coded” mode, (1) “intra coded” mode, (2) “inter not coded”mode and (3) “inter coded” mode; b) if the coding mode for P-VOP in theenhancement layer is one of “intra not coded” mode and “intra coded”mode, restoring pixels in a block of the enhancement layer (which isreferred to as “a enhancement layer block”) based on the coding mode;and c) if the coding mode for B-VOP is one of “intra not coded” mode,“intra coded” mode, “inter not coded” mode and “inter coded” mode,decoding the block of the enhancement layer based on the coding mode. 8.The method as recited in claim 7, wherein “intra not coded” mode meansthat the number of pixels in each enhancement layer block different frompixels of the lower layer is less than a reference value, in the case of“intra not coded” mode, the enhancement layer block is decoded based ona spatial prediction method, wherein in case of “intra coded” mode, theenhancement layer block is decoded based on an intra mode CAE method,wherein “inter not coded” mode and “inter coded” mode, no motion vectoris decoded for prediction of the enhancement layer block and the motionvector of blocks of the lower layer is utilized, wherein “inter notcoded” mode means that the number of pixels in each enhancement layerblock predicted from a previous video object plane (VOP) different frompixels of a current VOP is less than a reference value, and in the caseof “inter not coded” mode, a current block of the enhancement layerblock is decoded based on a temporal prediction method, and wherein incase of “inter coded” mode, the current block of the enhancement layeris decoded based on a inter mode CAE method.
 9. The method as recited inclaim 7, wherein the additional information for B-VOP in the enhancementlayer has a value described in a table as: Enhancement Layer Mode (0)(1) (2) (3) Lower (0) 1 01 001 000 Layer (1) 110 0 10 111 Mode (2) 00101 1 000 (3) 110 0 111 10


10. The method as recited in claim 9, wherein the coding modes (0), (1),(2) and (3) of the lower layer, in case they are the coding modes of thebase layer, are respectively mapped as follows: (0) all_(—)0 orall_(—)255 (1) intraCAE (2) MVDs==0 && No Update or MVDs!=0 && No Update(3) interCAE && MVDs==0 or interCAE && MVDs!=0.
 11. The method asrecited in claim 7, wherein the additional information for P-VOP in theenhancement layer has a value described in a table as: Coding mode Code“intra not coded” 1 “intra coded”
 01.


12. An apparatus for coding a scalable shape binary image by using acoding mode of an enhancement layer, wherein the scalable shape binaryimage has at least one enhancement layer including an enhancedresolution than that of a lower layer, said apparatus comprising:dividing means for dividing an image of an enhancement layer into blockshaving a predetermined size; determining means for comparing pixels ineach block of the enhancement layer with its corresponding pixels withinan area of the lower layer, and determining a coding mode of each blockof the enhancement layer based on the comparison result, wherein thecoding mode is one of (0) “intra not coded” mode, (1) “intra coded”mode, (2) “inter not coded” mode and (3) “inter coded” mode;transmitting means for, if the coding mode for P-VOP in the enhancementlayer is one of “intra not coded” mode and “intra coded” mode,transmitting the additional information representing its coding mode,and if the coding mode for B-VOP in the enhancement layer is one of“intra not coded” mode,“intra coded” mode “inter not coded” mode and“inter coded” mode, transmitting the additional information indicatingits coding mode; and coding means for, if the coding mode of theenhancement layer is “intra coded” mode, coding the enhancement layerblock based on a intra mode CAE method, and if the coding mode is “intercoded” mode, coding the enhancement layer block based on a inter modeCAE method.
 13. The apparatus as recited in claim 12, wherein “intra notcoded” mode means that the number of pixels in each enhancement layerblock different from pixels of the lower layer is less than a referencevalue, in the case of “intra not coded” mode, the enhancement layerblock is not encoded, wherein in case of “intra coded” mode, theenhancement layer block is encoded, wherein “inter not coded” mode and“inter coded” mode, no motion vector is encoded for prediction of theenhancement layer block and the motion vector of blocks of the lowerlayer is utilized, wherein “inter not coded” mode means that the numberof pixels in each enhancement layer block predicted from a previousvideo object plane (VOP) different from pixels of a current VOP is lessthan a reference value, and in the case of “inter not coded” mode, acurrent block of the enhancement layer block is not encoded, and whereinin case of “inter coded” mode, the current block of the enhancementlayer is encoded.
 14. The apparatus as recited in claim 12, wherein ifthe coding mode is “intra coded” mode, the coding means codes theenhancement layer to generate a first coded data and the transmittingmeans transmits the additional information indicating “intra coded” modeand the first coded data, wherein the first coded data is generatedbased on a intra mode CAE method; and wherein if the coding mode is“inter coded” mode, the coding means codes the enhancement layer togenerate a second coded data and the transmitting means transmits theadditional information indicating “inter coded” mode and the secondcoded data, wherein the second coded data is generated based on a intermode CAE method.
 15. The apparatus as recited in claim 12, wherein theadditional information for B-VOP in the enhancement layer has a valuedescribed in a table as: Enhancement Layer Mode (0) (1) (2) (3) Lower(0) 1 01 001 000 Layer (1) 110 0 10 111 Mode (2) 001 01 1 000 (3) 110 0111 10


16. The apparatus as recited in claim 15, wherein the coding modes (0),(1), (2), and (3) of the lower layer, in case they are the coding modesof the base layer, are respectively mapped as follows: (0) all_(—)0 orall_(—)255 (1) intraCAE (2) MVDs==0 && No Update or MVDs!=0 && No Update(3) interCAE && MVDs==0 or interCAE && MvDs!=0.
 17. The apparatus asrecited in claim 12, wherein the additional information for P-VOP in theenhancement layer has a value described in a table as: Coding mode Code“intra not coded” 1 “intra coded”
 01.


18. A apparatus for decoding a scalable shape binary image by using acoding mode of an enhancement layer, wherein the scalable shape binaryimage has at least one enhancement layer including an enhancedresolution than that of a lower layer, said apparatus comprising: meansfor receiving additional information indicating a coding mode of theenhancement layer and determining the coding mode, wherein the codingmode is one of (0) “intra not coded” mode, (1) “intra coded” mode, (2)“inter not coded” mode and (3) “inter coded” mode; means for, if thecoding mode for P-VOP in the enhancement layer is one of “intra notcoded” mode and “intra coded” mode, restoring pixels in a block of theenhancement layer (which is referred to as “an enhancement layer block”)based on the coding mode; and means for, if the coding mode for B-VOP isone of “intra not coded” mode, “intra coded” mode, “inter not coded”mode and “inter coded” mode, decoding the block of the enhancement layerbased on the coding mode.
 19. The apparatus as recited in claim 18,wherein “intra not coded” mode means that the number of pixels in eachenhancement layer block different from pixels of the lower layer is lessthan a reference value, in the case of “intra not coded” mode, theenhancement layer block is decoded based on a spatial prediction method,wherein in case of “intra coded” mode, the enhancement layer block isdecoded based on a intra mode CAE method, wherein “inter not coded” modeand “inter coded” mode, no motion vector is decoded for prediction ofthe enhancement layer block and the motion vector of blocks of the lowerlayer is utilized, wherein “inter not coded” mode means that the numberof pixels in each enhancement layer block predicted from a previousvideo object plane (VOP) different from pixels of a current VOP is lessthan a reference value, and in the case of “inter not coded” mode, acurrent block of the enhancement layer block is decoded based on atemporal prediction method, and wherein in case of “inter coded” mode,the current block of the enhancement layer is decoded based on a intermode CAE method.
 20. The apparatus as recited in claim 18, wherein theadditional information for B-VOP in the enhancement layer has a valuedescribed in a table as: Enhancement Layer Mode (0) (1) (2) (3) Lower(0) 1 01 001 000 Layer (1) 110 0 10 111 Mode (2) 001 01 1 000 (3) 110 0111
 10.


21. The apparatus as recited in claim 20, wherein the coding modes (0),(1), (2) and (3) of the lower layer, in case they are the coding modesof the base layer, are respectively mapped as follows: (0) all_(—)0 orall_(—)255 (1) intraCAE (2) MVDs==0 && No Update or MVDs!=0 && No Update(3) interCAE && MVDs==0 or interCAE && MvDs!=0.
 22. The apparatus asrecited in claim 18, wherein the additional information for P-VOP in theenhancement layer has a value described in a table as: Coding mode Code“intra not coded” 1 “intra coded” 01